A beautiful, crisp, finely-detailed photo will always be appreciated for its visual presentation, regardless of the photographer, subject, or ability of the viewer to put into words what exactly makes it a "nice picture."
That said though, visual presentation alone does not always translate to $$$ when a piece goes up for sale, which is the angle it sounds like you are approaching this question from. Subject matter is important, in that a photo of a HOFer will almost always bring more than a similar one of a "common" player, and all else being equal, photos shot by "known" photographers also tend to bring more.
I know you get all that already, but another factor to consider is the notoriety of the image itself. One of the reasons that everyone, even those who are not sports enthusiasts, will recognize Conlon's photo of Cobb sliding, or Fein's photo of Babe Ruth bowing out, is that they were recognized as being top-tier images from the start and have been used and reused and reprinted and seen over and over and over, so that the original works that those countless iterations were derived from have been elevated to iconic status. They are not just images OF icons, but rather the images themselves are iconic. That kind of notoriety takes time and exposure to imprint on the general consciousness. So while I think it would certainly be possible to find a new photo that SHOULD rival the old icons in terms of the "four C's" and notoriety of the photographer, I think any newcomer would have difficulty in challenging an original iconic photo in terms of price realized at auction.
That doesn't mean that they would be "judged harshly" or go unappreciated. I just don't think it would be possible for a new image to supplant one of the "old guard" in the public consciousness so quickly, if at all. As Mike's top pick illustrates though, you don't have to have the "best"/most-well-known photo to have a darn nice one that will turn the head of anyone who encounters it and/or bring a handsome sum on the auction block.
Just my 2 cents. And just so you know, you're killin' me, Bill
